The Adolescent Brain and Cognitive Development (ABCD) Study is the largest study of its kind to date. This landmark study began in 2016 as a collaborative effort by top researchers across the United States to enroll and follow 11,000+ healthy children from age 9-10 into early adulthood. The project will measure brain maturation in the context of social, emotional and cognitive development. This study has enormous potential to inform prevention, treatment intervention, and public health strategies for mental health and substance use.